1. Field of the Invention
The present invention relates to a projection type video display apparatus such as an LCD (Liquid Crystal Display) projector or a DLP (Digital Light Processor) projector.
2. Description of the Background Art
In projection type video display apparatuses utilizing display devices such as LCDs and DLPs as light valves, a system for controlling the brightness of a light source lamp depending on the characteristics of an image to be displayed to improve a visual contrast feeling has been proposed. Specifically, a system for detecting the peak value of an image signal or the average video level of the image signal, to judge the characteristics of an image and control the brightness of a light source lamp depending on the results of the judgment has already been developed (see JP-A-06-160811 and JP-A-03-179886).
Furthermore, as a system for controlling the light source lamp within the projection type video display apparatus and a cooling fan for cooling optical components and so on, a method of sensing the internal and external temperatures of the projection type video display apparatus using a temperature sensor and controlling the rotational speed of the cooling fan on the basis of the sensed temperature has already been developed (see JP-A-2002-72170).
As the light source lamp in the projection type video display apparatus, ultra-high pressure mercury lamps called a UHP (Ultra High Pressure) lamp and a UHE (Ultra High Efficient) lamp have been generally used. The lamps are characterized in that they have high luminescent efficiency. In order to maintain the high luminescent efficiency of the lamp as well as to keep the life thereof long, however, it is important to manage the temperature of a luminescent portion. In an example of a certain lamp, a burner must be managed such that the temperature thereof is 950±50°. Even if the temperature is increased or reduced too much, the life is liable to be shortened.
In a general projection type video display apparatus, the brightness of the light source lamp is always kept constant. By fixing the rotational speed of the cooling fan for cooling the light source lamp to the most suitable value depending on the internal and external temperatures of the projection type video display apparatus, therefore, the temperature of the luminescent portion can be relatively simply managed.
On the other hand, in the projection type video display apparatus for controlling the brightness of the light source lamp depending on the characteristics of an image to be displayed, when the rotational speed of the cooling fan for cooling the light source lamp is fixed depending on the internal and external temperatures of the projection type video display apparatus, cooling is insufficient in a case where the light source lamp is controlled in the direction in which it is brightened, while being excessive in a case where it is controlled in the direction in which it is darkened, thereby causing the life of the light source lamp to be shortened.